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neglects the full range of possible future temperatures . A recent global analysis of numerous factors involved in the energy demand predictions showed a weak agreement in these projections for hot and cold days . To go further , the future temperature being highly variable among climate projections , the uncertainties related to climate need to be quantified and included in estimates of future energy demand . A consistent global analysis of these uncertainties is still missing .
This new study focuses on proxies of the climate-driven energy demand for heating and cooling buildings and presents a global analysis of future trends together with a comprehensive analysis of uncertainties linked to temperature projections . To this end , the proxies of the climate-driven energy demand derived from the Degree-Days methodology are calculated using the simulated surface air temperatures of 30 CMIP5 ( Coupled Model Inter-comparison Project phase 5 ) general circulation models ( GCMs ) and two pathways of future greenhouse-gas concentrations .
We show that the increasing trends in cooling energy demand are stronger than the decreasing trends in heating with the MMM of all 30 models . However , where the trends in cooling are the strongest , the variability of the trends between individual models is high , making estimates of future energy demand uncertain in these regions .
RESULTS
• Proxies of climate-driven energy demand HDD and CDD calculated with the temperature of historical climate simulations have been validated against observations . We define our heating and cooling — climate-driven energy demand — proxies as the annual HDD and CDD sums calculated from daily mean , minimum and maximum temperatures following the UK Met Office methodology for each of the 30 CMIP5 climate simulations .
The advantage of HDD or CDD annual sums is that they can be compared on a global scale , regardless of the timing and length of local heating and cooling seasons . The heating and cooling proxies are presented for the MMM as averages over three 20-year periods 1941 – 1960 , 1981 – 2000 and 2021 – 2040 ( Supplementary Fig . 1 ). The spatial patterns of the MMM of the heating and cooling proxies are closely linked to the MMM of temperature on a global scale ( comparing Supplementary Fig . 1 and Supplementary Fig . 2 ). The decrease in HDD and the increase in CDD between the three studied time periods are also consistent with the underlying temperature increase .
Our results show typical values of the heating proxy over land areas between 0 and 1 500 HDD in inter-tropical regions ( from 30 ° N to 30 ° S ), between 1500 and 5000 HDD in midlatitude regions ( from 60 ° N to 30 ° N ; or from 60 ° S to 30 ° S ) and above 5000 HDD in polar regions ( above 60 ° N or 60 ° S ). Values of the cooling proxy are between 400 and 2 000 CDD in inter-tropical regions , and between 0 and 400 CDD in mid-latitudes . These values change in a warming world . However , the magnitude of the changes is not globally uniform ( Supplementary Fig . 1 ).
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RACA Journal I February 2022 www . hvacronline . co . za